Discharge apparatus



Feb. 27, 1940. L. D. MILES 2,192,047

DISCHARGE APPARATUS Filed Feb. 2, 1939 Lawrence D. Miles y rlmttorney.

Patented Feb. 27, 194

UNITED STATES PATENT OFFICE DISCHARGE APPARATUS Lawrence D. Mil es, Ballston Lake, N. Y., assignor to General Electric Company, a corporation of New York 2 Application February ,2, 1939, Serial No. 254,155,

4 Claims.

The present invention relates to means for improving the operation of power discharge devices. While not limited thereto, the invention is primarily applicable to devices having cathodes plifying the problem of heat dissipation. How

ever, if a cadmium tube is to be operated in a conventional circuit, it has heretofore been necessary to provide means for'preheating it in order to assure the existenceof sufficient cadmium l5 pressure to permit startingofthe tube.

My present invention provides means for avoiding this necessity, at least in connection with cadmium tubes which utilize a holding-arc to maintain the cathode spot. This result is ac? complished by supplying holding-arc current of greaterthan normal intensity during initial starting periods and by automatically decreasing such current upon the attainmentof a predee tel-mined temperature condition.

The features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof may best be understood by reference to the following de-;

scrip-tion taken. in, connection with the drawing in which" Fig. 1 shows the combination of a discharge device and circuit suitably embodying,

the invention; and Figs. 2 and 3 illustrate further applications of the invention. Referring particularly to Fig. 1 there is shown a sealed metal enclosure Ill having therein a main anode II and a cathode l2. The cathode is to be understood as being constituted of cadmium and is in direct contact with the envelope ill. The anode H is insulated from the envelope by means of an insulating ring I4 from which it is supported. Heavy current conductors l6 andcome sufficiently high to cause danger of a backfire occurrence. Consequently, it is readily possible to operate a cadmium-cathode device at a temperature on the order of say, 250 degrees centigrade, whereby effective heat dissipation 5' may be accomplished by: air cooling and without the need for a special cooling fluid such as water.

In the device illustrated in Fig. l, in addition to themain anode ll,'there are provided two keep-alive electrodes I9, 20, which serve in com- 10,

bination with an A. C. supplyto maintain a holding-arc to the cathode surface. These keep-alive electrodes are insulatingly supported from the top of the envelope iii by means of lead-in seals 2| and 22. a single anode supplied from a direct current source.

The holding-arc current required to maintain a cathode. spot during normal operation is madequate for this purpose when the device is cold, v I

working temperature. The means by which this 0: is accomplished may best be understood by re.

ferring to the energizing circuit shown in the' drawing. 5 v

The holding-arc current is supplied by means of a transformer 24 which has the terminalsof itssecondary respectively connected to the elec-v trodes l9 and 20. The midpoint of this secondary, is connected to the cathode l2 by being grounded to the envelope H] as indicated at 25. In series with the grounding connection there is provided a resistance heater 2'! which is thermally associated with the anode H and the function of I which will be more fully explained hereinafter. For initially starting thecathode spot, one may employ an immersion starting electrode of the character describedin Slepian and Ludwig Patent No. 2,069,283, granted February 2, 1937.

An electrode of this type is indicated in dot-' ted outline at 28. With the circuit arrangement so far described, it will be seen that as alternating current is supplied to the transformer 24 from a suitable source (not shown), full wave rectification occurs so that current flows from the cathode I2 first to one holding anode and then to the other, thus maintaining the They may be replaced, of course, by 15- the heater 21.

cathode spot. The circuit impedance is such that during starting operation, when the. cathode I2 is cold, the magnitude of the holding are current is nevertheless great enough to sustain the cathode spot. In order that the holding are current may be reduced to a more economical value when the device has reached its normal operating temperature, there is provided a temperature-responsive control means in good heat-exchanging relationship with some portion of the device. In the arrangement illustrated, such a control means, indicated by the numeral 29, is shown as being positioned in the vicinity of the anode l i so as to be affected mainly by the temperature of that element.

The device 29 may include, for example, a thermostat having a stationary contact 300 and a movable contact-bearing element 3| which is adapted to flex under the influence of heat. The movable element should be so biased as to be open when cold and to close when hot. In circuit with the temperature-responsive device and under the control thereof, there is provided a suitable circuit-regulating apparatus illustrated by way of'example as a saturable core reactor 33. This includes a load winding 34, a saturating or control winding 35 and a saturable core 35. The winding 35 is in shunt with the thermostat contacts 30, SI and carries the holding arc current when these contacts are open. Instead of a saturable core reactor, one may, of course, employ some other type of variable impedance element, such, for example, as a controllably conductive discharge tube.

From a consideration of the foregoing, it will be understood that the impedance presented by the regulating apparatus 33 is lowest when the core 36 is in its saturated condition; that is to say, when the contacts 30, 3! are open. Since this condition corresponds to a starting period of the discharge device, the holding arc current is necessarily greatest when this condition obtains. However, as soon as the temperature of the envelope H] has increased sufficiently to cause the contacts to close, thereby shorting the saturated winding 35, the impedance of the reactor increases and the holding arc current is correspondingly decreased. The decreased current will nevertheless be sufiicient to maintain the cathode spot because of the increased tempera- ,ture of the-cathode 12.

In order to hasten the temperature rise of the discharge device and also as a precaution against the possibility of cathode material condensing on the anode, I may employ the resistance heater 21. By acting directly on the anode Hi this heater indirectly affects the general temperature of the discharge device as a whole. In order that the heater 2! may be controlled in a desired manner, I prefer to connect it in series with the holding arc circuit as shown so that its temperature is proportional to the holding arc current. With this arrangement the action of the control device 29 in decreasing the holding arc current is simultaneously effective to reduce the supply of heating current to This is a desirable result since the normal action of the load current may be relied upon to maintain the temperature of the device at a desired level as soon as a stable operating condition has been attained. Of course, if the temperature of the device falls again for any reason, as, for example, because of a temporary shut down, the control means described will operate automatically to increase the energization of the heater.

In some cases, it is desirable not only to decrease the heat supplied to the device after a normal operating condition has been reached.

but also to provide means for additionally cooling the device so as to accommodate greater load currents. The control system which I have described may also be employed to place-such a cooling system in operation concurrently with the deenergization of the heating means and the reduction of the holding arc current.

In Fig. 2 I have illustrated one arrangement by which the result last indicated can be accomplished, In this case the holding arc circuit includesin addition to the heater 21, (indicated in dotted outline), a relay 40 which has its terminals in normally closed position. This relay in turn controls the energization circuit of a fan 42 or other cooling means provided in connection with the envelope It). With the circuit connection shown, as long as the holding-arc current is maintained at its initial or starting value the relay 40 will be held open. However; as soon as the control device 29 operatesto decrease the holding arc current the relay 40 will close, putting the fan 42 in operation. As previously explained in'connection with Fig. 1 the anode heating current will be simultaneously reduced to alowvalue.

The feature described in the foregoing is applicable to any means for controlling the supply of cooling medium to the discharge device and in Fig. 3 I have shown its application in connection with a mechanical control.

relay 40 of Fig. 2, acts to open-and close a valve In this case, I) a relay 45, which corresponds in function to the 46 provided in a conduit 41 through which-cooling fluid is supplied to the device Hi. It will be understood, of course, that the arrangement is I such that the valve 46 is closed during startingperiods but is opened by the action of the relay 45 as soon as the holding arc current is decreased. 1

While I have described my invention in connection with particular embodiments thereof, numerous modifications may be made by those skilled in the art without departing from the invention. For example, the control means for the heating current and the holding-arc may be made to provide a continuous inverse variation of these quantities with temperature. I, therefore, aim in the appended claims to cover-all such equivalent variations as fall within the true'scope of the foregoing disclosure.

fill:

What I claim as new and desire to secure by' Letters Patent of the United States is 1. In combination, a discharge device having a main anode, a cathode and means for producing a continuous holding arc to the cathode, the

a main anode,a cathode, and means for producing a holding arc to the cathode, the cathode being of such character that the current required to sustain an arc thereto is a function'of cathode temperature,

a resistance heater in heat- 5 exchanging relation witha portion of the device,

means for supplying a relatively intense holdingarc current during starting periods of the device and for supplying a predetermined heating current to the heater during such periods, and temperature-responsivemeans for automatically and simultaneously decreasing both, the holdingarc current and the heating current upon the attainment of a desired temperature condition.

3. In combination, a discharge device having a main anode, and a cathode comprising a mass of cadmium, a resistance heater thermally associated with the device, a circuit for, establishing a holding arc to the cathode, means for supplying current serially to the said heater and holding arc circuits during an initial starting period, and means for substantially decreasing such cmrent upon the attainment of a desired temperature condition. I

4. In combination, a discharge device having a main anode, a cathode and a keep-alive electrode, the cathode being of such character that thecurrent required to maintain a holding arc thereto is a function of cathode temperature, means effective when energized to cool at least a portion of the device, means for supplying a relatively intense holding arc current to the keep-alive electrode during starting periods, and

' of the device.

LAWRENCE D. IWILES. 

